At present a great variety of articles from difficult-to-form metals and alloys are finding an ever wider application in various fields of science and technology. However, their industrial production is labor-consuming and involves substantial losses of difficult to obtain and expensive metals and alloys. For example, it is known to industrially manufacture bars of 35 to 40 mm in diameter from a number of heat-resistant nickel alloys subjected to rolling on duo mills, smaller bar sections being obtained by means of mechanical treatment.
Bar or wire stock from difficult-to-form metals, such as tungsten and molybdenum, is produced by means of open die forging or roll forging. Such processess are labor-consuming, involve high expenses and are characterized by hard working conditions and low production output. Unfavorable stress conditions of metal during forging or rolling on duo mills, accompanied by free expansion of metal, lead to the formation of cracks and lamination, also resulting in the nonuniform working of metal structure across the entire section of workpieces. This, in turn, requires additional mechanical treatment of such workpieces, resulting in substantial losses of expensive metals. As a consequence, the yield of finished product is considerably lowered and the desired quality of the finished product can not be ensured.
It has been found that difficult-to-form metals and alloys lend themselves readily to working in multiroll passes formed by three, four or more rolls arranged in one plane. Favorable stress conditions created in such passes enable all-round reduction of metal, thereby increasing plasticity of metals and alloys. The rolling effected in multiroll passes is characterized by substantially low degree of metal expansion and high degree of metal reduction per pass. These favorable features are conducive to the production of high-quality rolled products, such as bar sections and wires.
It should be mentioned, however, that the prior-art roll stand constructions with multi-roll passes are intended mainly for rolling low-alloy steels, being unsuitable for rolling difficult-to-deform metals and alloys which are characterized by high resistance to deformation, exceeding 4 to 8 times the resistance to deformation shown by low-alloy steels. The known roll stands with multiroll passes have a constructional disadvantage which resides in that the space adapted to accommodate the bearings of workrolls is rather limited. In widely known constructions of multi-roll pass mill stands the bearings are mounted on both ends of the axle which carries a workroll; hence these is a limited size of the bearings and, as a consequence, low load capacity of the workroll.
There are known mill stands which comprise a roll housing adapted to mount chocks provided with cantilevered axles. Mounted on the axles are workrolls which accommodate bearings resting on the said cantilevered axles. The axles are made hollow with a view to receive spindles which are connected with the workrolls through the intermediary of gear drives (cf. U.S.S.R. Inventor's Certificate No. 208,643).
The arrangement of the bearings within the workrolls in the roll stand mentioned above makes it possible to increase the bearings in size and, consequently, to increase loading capacity of the workroll.
In the known roll stand, however, the spindles are mounted in the hollow interior of the cantilevered axles, with the size of the spindle being limited by the axle interior space which, if increased, will result in the lower strength of the cantilevered axle.
The aforementioned disadvantage renders it impossible to supply a required torque to workrolls, which torque occurs in the process of rolling difficult-to-form metals and alloys.
What is required is a mill stand constructed so as to provide for such special arrangement of spindles relative to the work-roll carrying axles that, without increasing the roll stand dimensions, it will permit the workrolls to take up substantially higher degree of rolling load and relatively great torque to be supplied to said workrolls, thereby enabling rolling of difficult-to-form metals and alloys.